Adding the most infuriating scenario I've dealt with; unresponsive people.
I'm buying an Australium Scattergun from a fellow, after I drag 50 keys into the trade he goes offline and the trade is cancelled. I shoot him a PM and trade offer, he doesn't respond to either.
I see him start to play TF2, ask him if he's still selling me the scattergun. No response. He starts typing back a message, but erases it, so I know he's reading my messages. I don't want to be rude and but a different one, but he's driving me up the fucking wall, it's been almost 24 hours. I am irate O͡͡͡͡͡͡͡͡͡͡͡͡͡͡╮༼;´༎ຶ.̸̸̸̸̸̸̸̸̸̸̸̸̸̸̸̸̸̸̸̸̸̸̸̸̨̨̨̨̨̨̨̨̨̨̨̨.̸̸̨̨ ༎ຶ༽╭o͡͡͡͡͡͡͡͡͡͡͡͡͡͡་